The invention relates to power station monitoring and regulating concepts taking into account the further development of requirements for the operation of photovoltaic energy generation installations.
The expansion of renewable energies results in new requirements for the availability and operational reliability of energy supply networks as time-dependent fluctuations in energy demand are now accompanied by a fluctuating, hard-to-predict energy supply.
In order to ensure a highly available and stable supply network also for the future, the legislator and the association of energy network operators laid the legal and technical bases for integrating regenerative energy generation installations with more than 100 kWp as controllable power stations into the existing supply networks by adopting the amendment of the Renewable Energies Sources Act (EEG) (October 2008) and the Medium-Voltage Directive of the BDWE (January 2009).
This creates new requirements for the planning, system engineering and operation of photovoltaic power stations. A safe process control system and an intelligent power station management are particularly important for an efficient and cost-effective realisation.
Network operators have not yet been able to define uniform, detailed requirements for network security management, power station regulation, protective functions and the used process control interfaces. At present, this results in very different requirements depending on the voltage level of the network connection point and the responsible network operator. A consultation with the responsible network operator on the requirements for participating in network security management is therefore recommended when applying for network connection.
In general, installations with an installed capacity of more than 100 kW are required to participate in network security management. In this respect, the network operator may limit the active power supplied by the photovoltaic power station to a certain percentage of the power station's installed capacity (currently 100%, 60%, 30%, 0%) by specifying a capacity level. This is accomplished by means of a process control interface defined by the network operator to which the power station regulating system is connected. The network operator may have to be informed of the successful realisation of this specification via the process control system.
So far, capacity reduction has only been described in the art as pure control. This means, a set point command coming from the electric utility is directly sent to all inverters present in the power station, and all are reduced to the same percentage value. Due to losses in the internal power transfer within the power station and possible unavailability of inverters (e.g. units shut down for repair purposes), this causes yield losses beyond the required reduction.
The object of the invention is to provide a system which is free of the disadvantages of the state of the art.